The proposed project stems from autoradiographic observations on an active incorporation of tritiated inositol into phosphatidylinositol occurring in myelinated axons. (Gould, R.M., 1976, Brain Research 117, 169-174). This active metabolism seems somewhat specific as other phospholipid precursors, choline, ethanolamine and glycerol are at best poorly incorporated into lipid within axons. These observations are being extended to study axon-based lipid metabolism following nerve injury (crush and ligation). We are examining by autoradiographic methods the incorporation of lipid precursors, inositol and choline into growth cones and regenerating nerve processes, to see if local lipid synthesis may play an active role in nerve regeneration. We are also using quantitative studies to look for a possible Schwann cell to axon transfer of lipid, which may aid in axonal outgrowth. We have developed an alternative biochemical approach to study the enzymology of axon based lipid metabolism. This avenue involves a nerve ligation paradigm, which measures the accumulation of axonally transported enzyme proximal and distal to a ligature. The rate of accumulation of inositol transferase is linear for up to three days, and is inhibited by placing a ligation a cm proximal to block axoplasmic transport. Activity of choline phosphotransferase present mainly in Schwann cell cytoplasm also accumulates at a ligature. Its accumulation is not blocked by a proximal ligature, but is blocked by locally injected actinomycin D. These results support the finding that the metabolism of phospholipids within axons is limited. We are presently studying the possible axonal transport of three other enzymes, acyltransferase (phosphatidic acid synthesis), CTP phosphatidate cytidylytransferase (CDP:diglyceride synthesis), and phosphatidylinositol kinase (phosphatidylinositol phosphate synthesis). These enzymes are all important in phosphatidylinositol metabolism and the 'PI effect,' and should extend our knowledge on the occurrence of this effect in axons and nerve endings.